Architecture to Communicate with Standard Hybrid Fiber Coaxial RF Signals over a Passive Optical Network (HFC PON)

ABSTRACT

One or more overlay wavelengths are applied to a GPON architecture to provide sufficient, cost-effective forward bandwidth per home for targeted, unique narrowcast services to allow traditional HFC operators to use a PON architecture with their existing HFC equipment. A separate return path capability using a separate coaxial cable with RF signals to the GPON may also be used. This return capability may be provided either by a fiber optic link or coaxial link from the home.

This application claims the benefit of U.S. Provisional Ser. No.60/866,906 filed on Nov. 22, 2006, herein incorporated by reference inits entirety.

BACKGROUND OF THE INVENTION

Modern cable telecommunications systems are typically built with aHybrid Fiber Coaxial (HFC) network topology to deliver services toresidences and businesses. By using Frequency Division Multiplexing,multiple services on these systems are carried on Radio Frequency (RF)signals in the 5 MHz to 1000 MHz frequency band. The HFC topologycarries the RF signals in the optical domain on fiber optic cablesbetween the headend/hub office and the neighborhood, and then carriesthe RF signals in the electrical domain over coaxial cable to and fromthe home. The fiber optic signals are converted to and from electricalRF signals in a device called a fiberoptic “node.” In the coaxialportion of the network, the signal is split to different housing areasand then tapped off to the individual homes. The RF signals continue tobe transported through the home on coaxial cables and connected todevices in the home. Due to attenuation in the coaxial cable andsplit/tap losses, “RF amplifiers” are used periodically in the coaxialplant to amplify the electrical signal so they are at an acceptablelevel to be received by the devices at the home.

Information is transported from the headend/hub office to the home, suchas video, voice and internet data, over the HFC network. Also,information is transported back from the home to the headend/hub office,such as control signals to order a movie or internet data to send anemail. The HFC network is bi-directional, meaning that signals arecarried on the same network from the headend/hub office to the home, andfrom the home to the headend/hub office. The same coaxial cable actuallycarries the signals in both directions. In order to do this, thefrequency band is divided into two sections, “forward path” and “returnpath”, so there is no interference of signals. The “forward path” or“downstream” signals, which typically occupy the frequencies from 52 MHzto 1000 MHz, originate in the headend or hub as an optical signal,travel to the node, are converted to electrical RF in the node, and thenproceed to the home as electrical signals over coaxial cable.Conversely, the “return path” or “upstream” signals, which typicallyoccupy the frequencies from 5 MHz to 42 MHz, originate in the home andtravel over the same coaxial cable as the “forward path” signals. Theelectrical signals are converted to optical signals in the node, andcontinue to the hub or headend over fiber optic cables.

The HFC network is capable of carrying multiple types of services:analog television, digital television, video-on-demand, high-speedbroadband internet data, and telephony. Cable Multiple System Operators(MSOs) have developed methods of sending these services over RF signalson the fiber optic and coaxial cables. Video is transported usingstandard analog channels which are the same as over-the-air broadcasttelevision channels, or digital channels which are usually MPEG2 signalover a QAM channels. The most common method for carrying data services,telephony services and sometimes video, is Data-Over-Cable ServiceInterface Specification (DOCSIS). In order to transport information onRF signals, the MSOs have a significant amount of equipment thatconverts the services so they can be carried on RF signals. Examples ofthis equipment would be Cable Modem Termination Systems (CMTS), QAMmodulators, Upconvertors and Digital Access Controller (DAC). Also,devices in the home are required to convert the RF signals to signalsthat are compatible with television sets, computers and telephones.Examples of these devices are television set-top boxes, cable modems andEmbedded Multimedia Terminal Adapter (EMTA). These devices select theappropriate forward path signals and convert them to usable signals inthe home. These same devices also generate the return path signals tocommunicate back to the headend/hub office. MSOs have a significantinvestment in the equipment at the home and headend/hub offices thatutilize DOCSIS and similar protocols. They also have a significantnetwork operation investment to manage this type of network with regardsto maintenance and customer service.

Today, the MSOs are facing competition from traditionaltelecommunication companies. These companies are utilizing newtechnologies where fiber optic cables are laid very close to the home,called Fiber-to-the-Curb (FTTC), or all the way to the home, calledFiber-to-the-Home (FTTH). With these technologies, many more servicesand higher quality can be delivered to the homes, while also loweringthe maintenance cost of the network because the active components arereduced. A common type of FTTH network is Passive Optical Network (PON)where no active components exist between the headend/hub/central officeand the home. There are several types of PON's including Broadband PON(BPON) and Gigabit-capable PON (GPON) which are actively being deployedby telecommunication companies in the United States. The technicalstandard for the BPON is defined in ITU-T Recommendation G.983 and forthe GPON is defined in ITU-T Recommendation G.984. For the sake of thisdisclosure, the GPON will be used as the reference since this is thelatest PON architecture being actively deployed, but this invention canapply to other forms of PONs.

FIG. 1 shows a typical architecture for a GPON and FIG. 2 shows atypical ONT for a GPON. As illustrated in FIG. 1, a forward path of atypical GPON network contains headend 1 with a broadcast transmitter 4and optical amplifier 6, and a wave division MUX/deMUX 8, which providescommunication to a 1×n optical coupler 9 at node 10 over optical fiber 3to couple n homes 12 to the communication signal. At the home 12, anOptical Network Termination unit 11 (ONT) converts the optical forwardsignals via optical triplexer 14 containing receivers 15 and 17 andtransmitter 16. Interface module 13 provides the Ethernet signals toEthernet output 19 for internet data, the POTS signals to RJ11 twistedpair wires 18 for telephone, and broadcast signals to coaxial cableoutput 20 for television (if the video overlay is used). In the returnpath, the ONT converts the Ethernet input and RJ11 twisted pair to anoptical baseband digital signal. Any television return signals utilizethe Ethernet input. At the headend/hub/central office, the GPON utilizesthe OLT 2 system as the interface between the PON and network-side.

Instead of using DOC SIS and similar protocols like an HFC network, theGPON utilizes baseband digital protocol for forward path and return pathsignals. The forward path baseband digital signals carry internet data,telephony and sometimes television service by using Internet Protocol(IPTV). The GPON also has an option for a forward overlay wavelength toprovide enhanced services to the home. Often, the overlay wavelength isat 1550 nm and delivers video services in the forward path usingFrequency Division Multiplexing just as the HFC network. This overlaywavelength is shared over many homes, up to 10000. Unlike the HFCNetwork though, the only option for return signals on the GPON is usingthe baseband digital return signal. Because of the method thatinformation is transported, the GPON utilizes vastly different equipmentat the home and headend/hub/central office 1 compared to HFC network.

MSO's cannot utilize their current methods of transporting informationover a PON, and therefore cannot utilize their current headend/hubequipment and home devices in this architecture. In order to competewith the telecommunication companies, MSOs would like to migrate to FTTHnetworks, such as GPON, to offer perceived and real increases inservices and quality. MSOs have a very large investment in DOCSIS andsimilar equipment at the headend/hub office and the home, which cannotbe utilized in a GPON network. Also the network management systems formaintenance and customer service are built around DOCSIS equipment and,therefore, running a second system in parallel would be costly.

Technical issues exist for utilizing the MSO's current infrastructureequipment in a GPON network. For example, the GPON network cannotprovide sufficient, cost-effective forward bandwidth per home fortargeted, unique narrowcast services if they are transported using theoverlay 1550 nm wavelength. To be cost-effective, the GPON overlaywavelength is split many times and feeds many homes, up to 10000, withthe same signal. This is acceptable in current GPON deployments becauseonly broadcast video services are transported on the overlay wavelength,and all narrowcast services, such as internet data and telephony, aretransported on the baseband digital signal. In order to use theircurrent infrastructure, the MSO would also transport narrowcast servicesusing RF signals on the overlay wavelength in the forward path. But inthis scenario, all homes would share the same narrowcast bandwidth whichwould severely limit the amount of unique services available for eachhome.

Further, the MSO's current equipment converts information to be carriedover RF signals in the return path. GPON has no option to carry RFsignals in the return path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary GPON architecture with broadcast overlaywavelength.

FIG. 2 illustrates an exemplary GPON ONT with broadcast overlaycapability.

FIG. 3 illustrates an exemplary GPON architecture with the broadcast andnarrowcast overlay wavelengths in the forward path.

FIG. 4 illustrates an exemplary modified GPON ONT with a second opticalreturn transmitter.

FIG. 5 illustrates an exemplary architecture with broadcast andnarrowcast overlay wavelengths and second optical return signal.

FIG. 6 illustrates an exemplary modified GPON ONT with a coaxial returnRF signal.

FIG. 7 illustrates an exemplary architecture with broadcast andnarrowcast overlay wavelengths and electrical coaxial return RF signal.

FIG. 8 illustrates an exemplary migration to GPON.

DETAILED DESCRIPTION

This disclosure utilizes multiple approaches to solve the aboveproblems. These approaches can be used together or separately in anetwork. In one approach a second overlay wavelength is added to theGPON architecture so it can provide sufficient, cost-effective forwardbandwidth per home for targeted, unique narrowcast services. Theinvention may also or alternatively add return path capability using RFsignals to the GPON. This return capability may be provided either by afiber optic link or coaxial link from the home.

FIG. 3 illustrates an exemplary architecture with the broadcast andnarrowcast overlay wavelengths in the forward path. In this embodiment,another overlay wavelength is inserted into each 1550 nm PON port fromthe optical amplifier in the headend/hub/central office 1 via narrowcasttransmitters 202, which may be QAM transmitters. This wavelengthcontains the unique, targeted narrowcast services and the number ofhomes sharing this signal is much smaller, for example, as few as 32homes, so the available bandwidth per home is significantly more thanprovided in a traditional GPON network. A narrowcast transmitter 202 isused to generate this second overlay wavelength, which is wave divisionmultiplexed at MUX/deMUX 8 with a broadcast signal provided by broadcasttransmitter 4 and amplifier 6. A narrowcast transmitter is generallydefined as fiber optic device that transmits only up to 400 MHz oftargeted services delivered on QAM channels, and it is much lessexpensive than a broadcast transmitter which requires much higherperformance. The narrowcast overlay wavelength is offset from the 1550nm broadcast overlay wavelength so it can be efficiently combined withthe 1550 nm wavelength, but it would still be passed along with the 1550nm wavelength through optical passives in the GPON. A wavelengthdivision multiplexer (WDM) is used to insert this wavelength with the1550 nm broadcast at the headend/hub/central office. ONT 311 providesthe broadcast and narrowcast signals to the user through ports 18, 19and 20.

The inventors provide two techniques for transporting RF signals in thereturn path. One is to add an analog return transmitter to the ONT andadd a second fiber optic link to the GPON so return RF signals aretransported from the home to the headend/hub office. Another is to add acoaxial cable link to the GPON to carry the return RF signals from thehome to an optical node, and then to the headend/hub office.

FIG. 4 illustrates an exemplary modified GPON ONT with a second opticalreturn transmitter and FIG. 5 illustrates an exemplary architecture withbroadcast and narrowcast overlay wavelengths and second optical returnsignal. The modified GPON utilizes the coaxial cable in the home forboth forward path and return path signals, which may be the same way itis utilized in a HFC network. The ONT 411 is modified to include a RFdiplexer 172 and second return optical transmitter 171. The RF diplexer172 splits off the return RF signals (typically from 5 MHz to 42 MHz/65MHz) coming from the home. By using a pluggable RF diplexer, thefrequency range for the return signals could be changed (for example,from 5 MHz up to 105 MHz). These RF signals are directed to an analogtransmitter 171 which converts the RF signals from the electrical to theoptical domain. The wavelength of this second transmitter may be at anywavelength, but most likely 1310 nm or 1550 nm. FIG. 4 shows themodified GPON ONT with a second Optical Return Transmitter.

The analog optical return signal is transported from the home on asecond fiber optic cable 31. This is preferred because the opticalpassives in the GPON generally cannot handle a second return wavelength.This optical return signal is combined with optical return signals fromother homes using an optical coupler 512 (i.e. 1×32) in node 500. Thecombined signals then travels to the headend/hub office 502 and receivedby a return analog optical receiver 505 where it is converted to back toan electrical signal.

This embodiment may rely on the standard protocols used today by theMSOs such as DOCSIS, ALOHA, or similar protocols to allow for propertiming, data collision control, distance ranging and RF power, asappreciated by those of skill in the art.

This embodiment combines multiple return optical signals onto one fiber.The challenge with this is that if two or more return lasers aretransmitting at the same time, noise can be generated due to non-linearmixing of the two optical carriers. Also, lasers will typically generatenoise if they are not transmitting data, which would impact the abilityof the optical receiver to detect the return signal from the activehome. Accordingly, in a preferred implementation, the lasers are turnedoff if the transmitters are not receiving RF signals from the home, andturned on when the transmitter receives a RF signal from devices in thehome. By using the timing from the standard protocols, only one of thelasers in a PON group (32 homes) would be turned on and transmitting ata frequency at any given time.

FIG. 6 illustrates an exemplary modified GPON ONT with a coaxial returnRF signal and FIG. 7 illustrates an exemplary architecture withbroadcast and narrowcast overlay wavelengths and electrical coaxialreturn RF signal. Just like in FIGS. 4 and 5, the modified GPON utilizesthe coaxial cable in the home for both forward path and return pathsignals, which may be the same way it is utilized in a typical HFCnetwork. The ONT 611 is modified to include a RF diplexer 172. The RFdiplexer splits off the return RF signals (typically from 5 MHz to 42MHz/65 MHz) coming from the home. By using a pluggable RF diplexer, thefrequency range for the return signals could be changed (for example, to5 MHz to 105 MHz). The difference with FIGS. 4 and 5, is that the returnnetwork is similar to today's HFC network. These return RF signals arepassed through the ONT 611 to a coaxial cable 512 from the house to thestreet. The return signals from the home are combined with returnsignals from other homes through electrical RF tap couplers 713. Thesecombined returned signals eventually feed into an HFC-type optical node709. At node 709, the return RF signals are converted to the opticaldomain via transmitter 705 and sent to the headend/hub office 702.

A variation of this embodiment is to have the RF diplexer 172 externalto the ONT 611. This discrete RF diplexer is on the coaxial cable on thehome-side which splits off the return RF signals. The return RF signalsare routed from the ONT 611 on a coaxial cable that goes to the street.

Similar to FIGS. 4 and 5, this embodiment may also rely on the standardprotocols used today by the MSOs such as DOCSIS, ALOHA, or similarprotocols to allow for proper timing, data collision control, distanceranging and RF power, as appreciated by those of skill in the art.

FIG. 8 illustrates a migration of an HFC network to GPON. Theembodiments above leave intact the ONT components that handle the GPONdigital baseband signals for forward path and return path. These are notused in the initial deployment of this proposed embodiment if allservices are using RF signals in the forward and return path. If theseONT components are left intact, the architectures outlined above allow amigration to a GPON without a truck-roll to the home or replacing theONT. In order to do this, the GPON OLT 821 is added at the headend/huboffice 800 and the wavelengths are inserted or dropped using a WDM. Atthe home, computers are unconnected from the cable modem and connectedto the RJ45 port on the ONT 811 with CATS cable. The telephones areconnected to the RJ11 ports on the ONT. For video services, the set-topbox would likely need to be changed to be compatible with IP overEthernet. The secondary fiber optic link or coaxial link used for returnRF signals is no longer used but could be left in place for futurebandwidth capability.

As an extension of the inventions, the ONT components used for GPONdigital baseband signals could be removed for cost savings. If this isdone, the architecture cannot be migrated to a GPON or other type of PONwithout replacing the ONT.

The present invention allows MSOs to largely use their existing HFCnetwork architecture in a PON architecture. This allows the MSOs toutilize the benefits of a PON architecture in a cost effective mannerwhich takes advantage of their investment in their existingarchitecture. It also allows the MSO to use familiar operating andsignaling techniques in a PON architecture to maintain reliability ofservice which achieving extended bandwidth to customers.

Those of skill in the art will appreciate that the above embodiments maybe modified without departing from the sprit of the invention. Forexample, the RF signals in the return path may be carried over mediumother than a coaxial cable, such other communication cables, or eventwisted pair.

1.-15. (canceled)
 16. A system for inserting a narrowcast overlaywavelength in a passive optical network (PON), the system comprising aheadend including: at least one broadcast transmitter for generatingbroadcast optical signals for transmission using a broadcast overlaywavelength in a forward path, wherein the forward path transmits throughan optical fiber associated with the PON; a plurality of narrowcasttransmitters, each generating narrowcast optical signals using thenarrowcast overlay wavelength; and a multiplexer for inserting thenarrowcast overlay wavelength into a broadcast PON port for combiningthe narrowcast overlay wavelength with the broadcast overlay wavelength;an interface port for transmission of the narrowcast overlay wavelengthwith the broadcast overlay wavelength via the broadcast overlaywavelength through the optical fiber in the forward path, wherein thenarrowcast overlay wavelength is offset from the broadcast overlaywavelength.
 17. The system for communicating over a PON of claim 1,wherein the headend further comprises a return receiver which isconfigured to receive return signals from the passive optical network.18. The system for communicating over a PON of claim 1, furthercomprising an optical network termination (ONT) unit which convertsoptical signals to electrical signals at an endpoint of the passiveoptical network.
 19. The system for communicating over a PON of claim18, wherein the ONT unit includes an optical transmitter which transmitsa return optical signal over a different optical fiber than providesoptical signals.
 20. The system for communicating over a PON of claim19, wherein the ONT unit includes an RF transmitter which transmits areturn RF signal over a coaxial cable.
 21. The system for communicatingover a PON of claim 20, further comprising a node which includes anoptical transmitter which converts return RF signals to return opticalsignals for transmission to the headend.
 22. A method for inserting anarrowcast overlay wavelength in a passive optical network (PON), thesystem comprising: generating broadcast optical signals for transmissionusing a broadcast overlay wavelength in a forward path, wherein theforward path transmits through an optical fiber associated with the PON;generating narrowcast optical signals using the narrowcast overlaywavelength; and inserting the narrowcast overlay wavelength into abroadcast PON port for combining the narrowcast overlay wavelength withthe broadcast overlay wavelength; transmitting the narrowcast overlaywavelength with the broadcast overlay wavelength via the broadcastoverlay wavelength through the optical fiber in the forward path,wherein the narrowcast overlay wavelength is offset from the broadcastoverlay wavelength.
 23. The method of claim 22, further comprisingreceiving return signals from the passive optical network.
 24. Themethod of claim 22, further comprising converting optical signals toelectrical signals at an endpoint of the passive optical network. 25.The method of claim 22, further comprising receiving a return opticalsignal over a different optical fiber than provides optical signals. 26.The method of claim 25, further comprising receiving a return RF signalover a coaxial cable.
 27. The method of claim 26, further comprisingreceiving return RF signals from an optical network termination (ONT)unit.
 28. A wave division multiplexer for inserting a narrowcast overlaywavelength in a passive optical network (PON), the wave divisionmultiplexer comprising: a receiver for receiving narrowcast opticalsignals using the narrowcast overlay wavelength and receiving broadcastoptical signals using a broadcast overlay wavelength; a processor forinserting the narrowcast overlay wavelength into a broadcast PON portfor combining the narrowcast overlay wavelength with the broadcastoverlay wavelength, wherein the narrowcast overlay wavelength is offsetfrom the broadcast overlay wavelength; an output interface for providingthe narrowcast overlay wavelength with the broadcast overlay wavelengthfor transmission via the broadcast overlay wavelength through an opticalfiber in a forward path, wherein the forward path transmits through theoptical fiber associated with the PON.
 29. The wave division multiplexerof claim 13, further comprising an interface with a return receiverwhich is configured to receive return signals from the passive opticalnetwork.